Why Einstein may have got it wrong

A century after Albert Einstein published his most famous ideas, physicists will today commemorate the occasion by trying to demolish one of them.

Astronomers will tell experts gathering at Warwick University to celebrate the anniversary of the great man's "miracle year" that the speed of light - Einstein's unchanging yardstick that underpins his special theory of relativity - might be slowing down.

Michael Murphy, of the Institute of Astronomy at Cambridge University, said: "We are claiming something extraordinary here. The findings suggest there is a more fundamental theory of the way that light and matter interact; and that special relativity, at its foundation, is actually wrong."

Einstein's insistence that the speed of light was always the same set up many of his big ideas and established the bedrock of modern physics.

Dr Murphy said: "It could turn out that special relativity is a very good approximation but it's missing a little bit. That little bit may be the doorknob to a whole new universe and a whole new set of fundamental laws." His team did not measure a change in the speed of light directly. Instead, they analysed flickering light from the far-distant celestial objects called quasars.

Their light takes billions of years to travel to Earth, letting astronomers see the fundamental laws of the universe at work during its earliest days. The observations, from the massive Keck telescope in Hawaii, suggest the way certain wavelengths of light are absorbed has changed.

If true, it means that something called the fine structure constant - a measure of the strength of electromagnetic force that holds atoms together - has changed by about 0.001% since the big bang. The speed of light depends on the fine structure constant. If one varies with time then the other probably does too, meaning Einstein got it wrong.

If light moved faster in the early universe than now, physicists would have to rethink many fundamental theories. His conclusions are based on work carried out in 2001 with John Webb at the University of New South Wales in Sydney. Other astronomers disputed the findings, and a smaller study using a different telescope last year suggested no change.

Dr Murphy's team is analysing the results from the largest experiment so far, using light from 143 bright stellar objects. Einstein's burst of creativity in 1905 stunned his contemporaries. He published three papers that changed the way scientists viewed the world, including the special theory of relativity that led to his deduction E=mc².

The Physics2005 conference, set up by the Institute of Physics as part of its Einstein Year initiative, runs until Thursday.